This invention relates to a line of sight guidance system, and in particular, to a guidance system for a beam rider missile. While the invention is discussed in particular detail with respect to its missile control application, those skilled in the art will recognize the wider applicability of the inventive concepts disclosed hereinafter.
It further relates to a method for providing an encoded beam pattern by rotating the center of a reticle so that the reticle intersects the beam and coordinating the pulse repitition rate of the beam source with the reticle center position.
The prior art reveals a number of devices for aiming and guiding projectiles of various designs toward a target. One particular projectile design with which the invention disclosed hereinafter has particular application is described in the U.S. Pat. No. to Tucker, No. 3,868,883, issued Mar. 4, 1975. The missile disclosed in the Tucker patent includes means for positioning a missile along a line of sight and includes thruster elements, the firing rate and firing direction of which are controlled to position the missile. The electrical signals for firing rate and firing direction are generated at the launch site and transmitted to the missile along a physical connection between the launch site and the missile. While the apparatus disclosed in the Tucker patent works well for its intended purpose, there are instances where the physical connection between a launch site and the missile are undesirable. For example, missile travel over bodies of water cannot be conducted reliably because the connections between the site and the missile often will dip into the water, sometimes causing malfunction of the physical connections. Our invention is intended to be compatible with the projectile disclosed in the Tucker patent, although its application is not limited to that projectile type. Constructional features of the missile, while important in overall weapons system performance, are not described in detail. Details of the missile construction may be obtained from the above-referenced Tucker patent.
In general, our invention relates to a projectile or missile guidance system in which a frequency modulated encoded laser beam is projected to provide control of a beam rider missile in two degrees of motion. In particular, the system includes a laser beam pattern projector including a rotating reticle with a rotating center for chopping the laser beam. The laser beam source is pulsed at two different rates in synchronism with the angular position of the reticle center, thereby providing a binary coded coordinate grid and a reference data pattern which contains in itself all the magnitude and phase components necessary to define the location of the projectile in the grid pattern. The reticle center rotation and the rotation of the reticle about its center are phased so that noise components in the beam produced by mechanical and optical fabrication tolerances appear in the missile borne decoder at frequencies above the required missile control frequencies, and therefore may be removed easily, for example, by use of proper filters, during processing of the control signals. The projected power density of the beam at the range of the missile is held constant during most of the missile flight by the programming of a zoom lens to track the missile. Consequently, the sensitivity of the missile receiver to displacement in the grid also remains constant. The decoding devices carried by the missile include a single receiver and a decoder which separates the incoming beam signal into two channels, a first channel reference for establishing a phase reference signal, and a second, information channel containing the beam spatial frequencies for determining displacement and unreferenced direction of the missile from beam center. The phase reference signal is separated into vertical and horizontal (quadrature) signals that are multiplied with the information signal to produce error signals. The error signals are used to produce the necessary projectile control commands for positioning the projectile along the beam center.
The prior art reveals a number of devices for providing FM modulation of a projected beam. For example, the U.S. Pat. No. to Menke, No. 3,690,594, issued Sept. 12, 1972, discloses a frequency modulated beam generated by a rotating reticle having a nutating center. Our invention is distinguished from the Menke patent, and similar art in the field of our invention, in that phase reference lateral distance and direction data are transmitted in a single beam from a single projector. Because the beam contains all necessary information for position determination, only a single receiver is required for beam reception at the projectile. Consequently, the overall system design is simplified while the data link between the launch site and the missile is improved.
Our invention finds particular application in guided missile systems which require highly secure, accurate, low-cost guidance means for use against tactical targets. A typical anti-tank weapon application employing the guidance system of this invention can be made light enough to be carried and operated by one man. The missile system can be operated under either day or night lighting conditions. Of primary importance is the high degree of security against battlefield countermeasures which is achieved because the missile carries a single information input receiver/detector which accepts beam radiation energy only from the area behind the missile, and beam operation in a portion of the infrared frequency spectrum which is undetectable to the unaided eye. Detection of the beam by sophisticated detection devices at the target is made difficult by use of a low power beam which has its beam radiation energy spread over a large angle at the time of missile launch. The large beam angle at launch ensures missile capture by the beam, and initiation of missile guidance shortly after launch. The beam angle is decreased as the missile flies to the target, thus maintaining essentially constant beam power density at the missile throughout flight while minimizing the power density on the target. In addition, the variable beam angle simplifies missile electronic circuit design and permits the maintenance of guidance accuracy nearly independent of target range. The beam angle variation is provided by an optical system which incorporates a variable power field of view, commonly referred to as a zoom lens, and means for controlling the zoom lens drive in accordance with missile position.
One of the objects of this invention is to provide means for guiding a missile or other device along a line of sight path.
Another object of this invention is to provide improved means for controlling the flight of a projectile.
Another object of this invention is to provide a guidance system having improved accuracy for guiding a projectile towards a target.
Yet another object of this invention is to provide a line of sight guidance system which is relatively inexpensive, light weight, portable, and requires little or no special skill or training in its operation.
Yet another object of this invention is to provide a guidance system having a continuously generated beam projected by a single projector, which beam contains all data elements necessary for the determination of distance and direction from a point in the beam to the center line axis of the beam.
Another object of this invention is to provide a guidance system for a missile which provides approximately constant beam power density to the missile throughout the flight of the missile.
Still another object of this invention is to provide a missile guidance system that requires only a single receiver for reception of beam information at the missile.
Another object of this invention is to provide a guidance system utilizing a laser diode that is pulsed electronically at different rates during beam projection.
Another object of this invention is to provide a guidance system for a missile which provides approximately proportional changes in the spatial frequencies to the missile's receiver, as compared to the change in the lateral position of the missile throughout most of the missile's flight.
Other objects of this invention will be apparent to those skilled in the art in light of the following description and accompanying drawings.